CMOS image sensor (CIS) has been widely applied in electronic devices with image capturing function and digital camera. In general, the image sensor comprises a pixel sensing array, and the pixel sensing array comprises a plurality of pixel sensing unit arranged in an array. The pixel sensing unit comprises a light-sensing component, such as a photo diode or a photo transistor, and a converting circuit. The sensitivity of the pixel sensing unit is related/proportional to a light-sensing area of the light-sensing component. Take the pixel sensing unit comprising the photo diode as an example, the photo diode stores the electronic charges caused by the light in the potential well of the photo diode, and the electronic charges is converted by the converting circuit comprising transistors into voltage signal, where the voltage signal is the pixel value corresponding to the pixel sensing unit. Light sensitivity of the pixel sensing unit is related to an area of the photo diode in the circuit layout.
To achieve a specific light sensing capability for the image sensor, the pixel sensing unit is required to have a certain light sensing area. In the prior art, each pixel sensing unit only comprises a light sensing component. In other words, the only light sensing component of the pixel sensing unit has to have the required light sensing area of the pixel sensing unit. However, for the light sensing component with large light sensing area, the electronic charges within the potential well is not easy to be completely drained out by the converting circuit, such that the light-sensing component may have residual electronic charges, which may cause unnecessary image sticking effect on the digital camera. In addition, the image sensor comprises a collimator in general, configured to project the light onto the pixel sensing unit. However, the pixel sensing unit and the collimator are not perfectly aligned, such that crosstalk exists between light paths.
Therefore, it is necessary to improve the prior art.